The present invention relates generally to inspection systems for use in assessing the performance of industrial manufacturing processes, and more specifically to a nondestructive inspection system for assessing the quality of resistance spot welds.
Sheet metal joining processes are widely used in many industries including the aerospace and automotive industries. Among these processes, resistance spot welding is a very common procedure used to join metal sheets because it has high process speed and is easily adopted in mass production lines. Seam welding, weld bonding, adhesive joining, soldering, and brazing have also gained acceptance. The quality control of such joining processes has been recognized as an important issue to manufacturers. The quality of weld joints is affected by the joining process itself and by the design of the joint. Many factors are considered, including metallurgic reactions, thermal behaviors, chemical composition, starting condition of the base metal, welding and bonding conditions, and the welding and bonding equipment used during the process. Furthermore, the intricate relationship between these factors makes it difficult to control the quality of the weld joint and difficult to inspect the weld joint in a nondestructive manner.
Acoustic methods are commonly used nondestructive testing methods for various inspection applications. Unlike other nondestructive testing methods, acoustic methods provide both surface and internal information. Moreover, acoustic methods allow for deeper penetration into specimens and higher sensitivity to small discontinuities in a weld joint. Acoustic methods, however, do have limitations. The most significant limitations include the requirement of a skillful operator for using the testing device and analyzing acoustic data, as well as the very subjective nature of identifying a stuck or cold weld or inadequate bond, such as a kissing bond. Accordingly, the field of ultrasonic nondestructive evaluation (NDE) is in need of a reliable process or technique for identifying poor quality joints in a manner that eliminates the involvement of a skilled operator and the subjective interpretation of test data.